1. Cost Models

The cost models are being updated continuously by the T2D Team as more information becomes available. This documentation captures updates as of:

• 20 March 2025

Updated models:

• Aquaculture (3.7.0 CA-Production; 3.5.5 CA-Deployment)

• Larval slicks (3.9.2 LM)

This documentation links information and assumptions of cost models and ecological models (ReefMod, ADRIA, ~CScapeC~scape, CoCoNet) and required by the economic models (CREAM).

1.1 Aquaculture

1.1.1 Changes to previous generation of cost models:

• Cost model separated into two components: production and deployment models. Production
  and deployment occur in same year.

• Contingencies are removed from calculation – optional feature in post processing.

• Cost of aquaculture facilities is factored in as contracted service
  (based in Townsville).

• 2.5% sustaining capex removed from calculation (assumed to be internalised in
  contracted service).

• No volunteer vessels are deployed.

• Monitoring cost no longer included.

• Decommissioning costs still assumed to be zero (devices will not be removed).

• Deployment model requires choosing a specific reef (4 reefs are currently available),
  which are tied to specific ports (distance-based cost flexibility – vessel travel costs
  are included).

• Expansion requires additional CAPEX for production and deployment calculated in model.
  CAPEX_scale for production expansion for second batch less than CAPEX for first batch.
  Expansion costs cover tanks required, but don’t include construction costs for buildings to house them.

• All costs are estimated in A$2024 real value (best approximation).

1.1.2 Cost model information:

• The reefs used to harvest and deploy coral species are in close proximity.

• Species vs functional groups: each species and regional species variant must have
  separate tank; information required to determine the number of tanks: \

1. How many species?

2. Where was each species harvested and deployed?

• When producing new devices this is divided over number of spawnings and number of “batches” (one batch is one species in one region)

  • If a new species is introduced, there needs to be a trip out to the reef to do heat tolerance testing on that species

  • This is where corals are sampled in the field and their heat tolerance is tested

  • So if introducing a new species in later years, the testing cost needs to be included

  • There is an input for “New species batches” which includes testing costs

• Model requires an even distribution of number of devices/corals across all specified species. This might change with further cost model development and needs to be revisited.

• No additional costs of breeding corals with differentiated heat tolerances.

• ID setting: number of species (ID step previously completed  cost =0); number of new species (ID step must be completed  cost >0).

• Each device has 3 settlement units, with 8 settlers per unit; conditional on assumed survival rate, one device yields one 1-YOEC with an assumed survival probability. This probability includes all processes in the first year post deployment, including devices being carried away by currents and corals dying on the device.

• Assumed survival rate of larval settlers into 1-YOEC: 80% upper estimate; 60% lower estimate. 1YOEC are defined as corals after first year post-deployment – direct input into ecological model.

• For the deployment model, the Large vessels, such as the Large Tourism vessels, are the best estimate for cost of transport for now.

1.1.3 Assumptions:

• Maintenance cost assumed to be factored into production cost via contracts.

• Decommissioning cost assumed to be zero (devices will not be removed).

• Economies of scale assumed to be zero.

• Capacity limitations and potentially resulting cost changes assumed to be zero.

• Construction cost of buildings needed to house additional breeding tanks in case of expansions assumed to be zero.

• All costs are estimated in A$2023 real value (best approximation).

• Any other assumptions inherent in cost model [outside the scope of this study and not captured here].

1.2 Larval slicks

1.2.1 Changes to previous cost models:

• Contingencies are removed from calculation (optional feature during post processing).

• 1.5% sustaining capex removed from calculation (i.e., no maintenance costs included). Model assumes that after 10 spawning events (5 years given assumed 2 spawnings per year) initial CAPEX gets replaced in full.

• Expansion requires additional CAPEX calculated in model.

• No volunteer vessels are deployed.

• All costs are estimated in A$2024 real value (best approximation).

1.2.2 Cost model information:

• Settings ‘new domain’: if set to ‘yes’ assumes 1 months’ worth of research is costed; default would be ‘no’.

• Larval harvesting and deployment occur in spatial proximity (same reef).

• Input “Device deployment size” refers to the number of settlement devices

• Input “Larval release pools” refers to the number of pools for release rather than settlement

• Current models specify the different ship types for different parts of deployment – the “spawning block mothership” is used the longest and hence may have the most impact on costs.

• Input “Passive spawn catcher” should be generally left at 0%, the idea is to put out deflated larval pools to catch larvae passively over night with wind, but this is still being looked into.

• Currently no cost differentiation across different reefs.

• One device yields one 1-YOEC with an assumed survival probability. Larval survival rate set to 60% (based on recent research). This probability includes all processes in the first year post deployment, including devices being carried away by currents and corals dying on the device.

• Two methods of larval deployment (separate or joint application possible): 1) device-based method; 2) free-released method – no devices).

• Three vessel types required: 1) pre-spawning vessel (e.g., set-up, checks); 2) spawning mothership (larval harvesting); 3) spawning support ship (towing pools, moving over reefs to harvest larval). Use currently default settings for vessel types.

• Costs:

  • Pre-spawning work, modelling

  • Freight equipment to nearest port

  • [NOT COSTED] Travel from port to site

  • Set up pools

  • Spawning – collect larval slicks at midnight, transfer to pools

  • Wait around for the larvae to grow

  • Device settlement, larval release, device deployment

  • Pack up pools

  • [NOT COSTED] Return travel to port

  • Equipment washdown

  • Freight equipment back to storage

  • [NOT COSTED] Storage locker/s

1.2.3 Assumptions:

• Haulage of freight equipment to nearest port and back to storage assumed to be constant independent of location of storage facility and port used.

• Maintenance cost assumed to be zero during lifetime of equipment (5 years based on 2 spawnings per year).

• Cost of vessel travel from port to reef site and back assumed to be zero.

• Storage locker cost assumed to be zero.

• Economies of scale assumed to be zero.

• Capacity limitations and potentially resulting cost changes assumed to be zero.

• Any other assumptions inherent in cost model [outside the scope of this study and not captured here].